Overioad indicator



Jan. l, 1938. V, L DANlELS 2,105,410

ovERLoAD INDICATORy Filed July 5. 1936 E li Mya/dw, lv

atented Jan.. il, 1938 TE il STATES PATENT OFFICE ster Electric Company, Racine, Wis.,

ration of Wisconsin a corpo' Application July 3, 1936, Serial No. 88,846

4 Claims.

'I'he present invention relates to an overload indicator for amplifying circuits, such as public address amplifying systems, or the like.

In such public address systems, the speakers are usually located at a point remote from the controlling circuits, so that the operator is greatly hampered in the adjustment of the apparatus in order to secure a maximum efficiency or sound volume without overloading the apparatus. Without such an indicator, it would be necessary to have one person located at the loud speaker to advise the operator by some form of signal as to the operation of the loud speaker, eii'iciency, overload, distortion, or the like, so that a proper adjustment can be made by the operator.

One of the objects of the invention is the provision of an improved audio overload indicator or a visual volume level indicator which is adapted to be used in amplifier circuits to indicate the overload point of the amplifier output tubes of an amplifier circuit.

Another object is the provision of an improved electrical system of visually indicating the distortion level in connection with an audio amplier circuit.

Another object is the provision of a system of the class described which is adapted to utilize an electron ray tube, as, for instance, tubes of the indicator type which are commercially known as the 6 E 5 and 6 G 5, for the purpose of indicating overload in an audio circuit.

Other objects and advantages of the invention will be apparent from the following description and the accompanying drawing, in which similar characters of reference indicate similar parts -throughout the several views.

` be directly grounded;

Fig. 3 is a vertical elevational view with parts of the tube broken away, showing the electron ray tube of the indicator type, which is prefer- -ably used in thecircuits of Figs. 1 and 2;

Fig. 4 is a diagrammatic illustration of the appearance of the end of the electron ray tube "when the output tubes are not overloaded;

Fig. 5 is another view of the indicator; show- ""'ing theappearance of the indicator when the point of Overload or a maximum eiiciency been reached.

Referring to Fig. 3, the electron ray tube which has is utilized in the present indicating circuit is a high vacuum, heater-cathode type of tube designed to indicate visually, by means of a fluorescent target, the elects of a change in the controlling voltage. 5

Referring to the tube, I0 indicates the tube base, II the glass envelope, I2 the cathode, I3 the triode grid, I4 the uorescent target, I5 the triode plate, I6 the cathode light shield, andy II f the ray control electrode. The same elements 10 are correspondingly designated in the diagrams of Figs. 1 and 2, with the same numerals, the complete tube being indicated by the base numeral I0.

In addition to the elements mentioned, the 15 tube also has a heater filament I8. The ray control electrode Il is an extension of the triode plate, and therefore has no additional numeral in the wiring diagram.

The operation of an electron tube of this type 20 is well known, and need not be described in detail. The hot 4cathode I2 provides a source of electrons which are attracted to the positively charged target I 4, which is coatedwith a fluorescent material. Electrons impinging on the coated target, which are reflected to the target, cause the target to glow.

'I'he extent of the fluorescent area can be controlled by means of a third electrode placed between the cathode and target, comprising the 3o ray-control electrode I1.

'I'he pattern developed on the uorescent target depends on the contour of the target, as well as on the position and shape of the third electrode. With a frusto-conical fluorescent target I 4, as shown, and a\vertically extending control plate I1 located between the target and the cathode, thel patterns developed are substantially as shown in Figs. 4 and 5, including other patterns of greater or less area. 40

In addition to this, the shadows may actually overlap on overload of the circuit, when the ap-4 paratus is suitably adjusted.

Referring to Fig. 1, this is a diagrammatic illustration of the circuitand apparatus required for the application of the electron ray tube as a visual volume level or overload indicator for loud speaker.v The apparatus may comprise any suitable number of loud speakers I9, usually connected in parallel by suitable conductors, which are in turn connected by the conductors 20, 2|, to the terminals of the secondary of a transformer 22.

This transformer may be comprised in the amplier itself, as indicated by its inclusion in the 55 amplier 23 in Fig. 1, or it may be an external transformer, as indicated by its location external to the amplifier 2d, as shown in Fig. 2.

The transformer usually is the output transformer of the amplifier. One side of the transformer secondary, such as, for example, the conductor 2i, may be grounded by a conductor 25, and the secondary is provided with an adjustable tap 26, which is set for the right amount of voltage on the transformer secondary to close the shadow of the electron ray tube at amplifier overload point.

The tap 25 may lead to the plates 2l of a rectifier tube 23, the cathodes 29 of which are connected by a conductor 30 to a resistance 3i, which is connected to ground at 32. A conductor 33 leads from conductor 30 to a condenser 34, which is connected to another resistance 35, the opposite terminal of which is connected to ground at 32. A conductor 36 leads from a point between the condenser 34 and resistance 35 to the trlode grid I3 of the electron ray tube II).

'I'he heater filament 3T of the rectifier tube 28 is, of course, connected to an appropriate source of energization, and the heater filament I3 of the electron ray tube is also suitably energized. The electron ray tube cathode I2 may be connected by a conductor 38 to ground. The triode plate I5 may be connected through a resistance 39 to the target I4, which is connected to a high voltage source, such as a positive 250- volt battery, by conductor 40. Y

' Referring to Fig. 2, this is a circuit diagram, which may be used where the output of the amplifier cannot be directly grounded. In this case the amplier has its output conductor 2D connected to ground through a resistance 4 I. A conductor 42 extends from ground to'a condenser 43, the opposite terminal of which is connected by conductor 44 to the upper terminal of resistance 4I in Fig. 2` and extended to connect to the triode grid. In this case the adjustable tap 26 from the output transformer is connected up with the rectiiier tube 28 in exactly the same manner, and the cathodes 29 of the rectifier tube are connected to ground by conductor 45. It will thus be observed that all o f nthe other arrangements of the circuit are substantially the same as described with respect to Fig. .1.

The characteristics of the resistor 3| in. Fig. 1 and 4I in Fig. 2 depend upon the rectier load desired. The characteristics ofthe condensers 34 and 43 and the resistance 35 depend upon the time constant desired.

The operation of the circuit is as follows: The alternating current audio voltages in the output circuit of the amplifier are rectified by the rectiiler tube 23 and appear across the rectifier load resister 3l or 4I as pulsating direct current. 'I'his charges the condenser 34 or 43 by an ampunt depending upon the magnitude of these voltages.

In the circuit of Fig. 1 the negative voltage is taken from the resistance 35 for the grid of the electron ray tube operation. In the circuit of Fig. 2 the negative voltage is taken from resistance 4I for the grid of the electron ray tube operation.

This negative voltage in respect to the cathode of the electron ray tube causes the shadow to widen or to narrow in the electron ray tube according to the voltage variations in the rectifier load resister 3I or 4I;v By setting the A. C. applied voltage on the rectifier by means of the adjustable tap 26 at a proper point, the shadow on the electron ray tube can be made to close just amaai@ The electron ray tube, when used as an audio load indicator or a visual volume level indicator, works from the audio voltages in the audio ampliler by using a. very small portion of the power output of the amplier. When no power is being developed, there is no indication or movement of the shadow, and maximum movement of the shadow will indicate that more power is being developed by the amplifier. The shadow width is constantly changing with the variation of power output of the amplifier, and the voltage applied to the triode grid can be adjusted by adjusting the voltage applied to the rectifier so that the shadow on the electron ray tube closes at overload point of the amplifier output tubes.

It will thus be observed that the volume of the amplifier output may be conveniently adjusted with the apparatus of Figs. 1 or 2, so that a maximum volume is secured at the speaker by adjusting the volume to the overload point. as indicated by the electron ray tube.

. An indication of the type of Fig. 5 is exemplary of that when the output tubes arer approaching overload and the speakers are at maximum volume. This adjustment may be made by the operator without assistance from any other party, or

without any attention to the action of the loud public address system may be so operated with an indicator of the class described as to make the speech audible over the maximum amount of area or distance from the loud speaker, without any chance of the operator overloading the tubes or adjusting the volume to such an amount that there will be more than the permissible amount of distortion.

While I have illustrated a preferred embodiment of my invention, many modifications may be made without departing from the spirit of the invention, and I do not Wish to be limited to the precise details of construction set forth, but desire to avail myself of all changes within the scope of the appended claims.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent of the United States, is:

1. In anamplifier circuit, the combination of an amplifier with a remote speaker energized by said amplier, and an indicator for indicating the overload point of said amplifier, comprising an electron ray tube of the indicator type, said electron ray tube having its grid controlled by voltages derived from an outputcircuit of said amplifier,

g the voltage on said grid being so arranged that indicating the overload point of said amplifier,

aiutare comprising an electron ray tube of the indicator type, said electron ray tube having its gridcontrolled by voltages derived from the audio frequency circuit, `and rectied by a rectii'ler tube connected to a portion of the output transformer windings, and impressed upon a suitable resistance.

4. In an overload indicator for amplier circuits, the combination of an electron ray tube of the indicator type, with means for energizing the grid of the tube, with voltages controlled by the volume of current in the audio circuit, comprising a. speaker and an audio transformer having a primary and a secondary, suitable circuits from: the secondary of the transformer to said speaker, an adjustable tap on said secondary leading to a rectifier tube, the output of said rectier tube being connected to the grid of said indicator tube, means for energizing the other electrodes of said indicator tube, and means for connecting a return circuit from said indicator tube to said sec# ondary, the voltage on said grid being so adjusted that the indicator tube indicates the maxi- 10 mum permissible volume at the speaker. 

